The present development is a catalyst and method useful for the production of polyols. Specifically, the invention is directed to the use of a nickel on alumina-silica catalyst for the hydrogenolysis of carbohydrates. Optionally, the catalyst may be promoted with noble metals. The method comprises reacting a carbohydrate with hydrogen in an aqueous media in the presence of the nickel on alumina-silica catalyst
Polyols are commonly derived from sugars or carbohydrates. An aqueous solution of sugar is treated with hydrogen in the presence of a nickel catalyst to produce a sugar alcohol. The sugar alcohol, when further treated with hydrogen in the presence of the nickel catalyst, can be converted to polyols and glycols.
Because the media for these hydrogenation reactions is water, it can be challenging to identify an effective, relatively long-lived catalyst for these processes. One approach identified in the prior art was to use colloidal metal. This avoided the problem that many common catalyst supports are not stable in water. However, it was difficult and expensive to remove the colloidal metal from the resulting polyols and glycols. In U.S. Pat. No. 5,162,517 (issued to Darsow on Nov. 10, 1992), carrier-free catalysts are processed into mouldings from metal powders. The metal powders include elements of the iron group, such as nickel, cobalt, iron and mixtures and alloys of these metals. The mouldings comprise at least 70% metal.
Supported metal catalysts have also been proposed for use in carbohydrate hydrogenation processes. Silica-alumina carriers are known in the art, but the '517 patent found these to be problematic: “nickel catalysts on a carrier (SiO2/Al2O3) [have] extremely high active surfaces of 140-180 m2/g so that the catalysts are so active that they must be stabilized by additional chemical treatment methods . . . . However, the deactivating stabilization of the catalyst then requires such high reaction temperatures during the hydrogenation of sugars (130-180° C.) that uncontrollable side reactions can occur . . . . ” In U.S. Pat. No. 4,380,678 (issued to Sirkar on Apr. 19, 1983), a nickel on silica-alumina catalyst is used in a process for the catalytic conversion of monosaccharides to polyols. However, the process is a multi-stage process and has a relatively low conversion rate. In the process of the '678 patent a monosaccharide feedstream is initially reacted with hydrogen at a temperature of from 130° C. to 180° C., and then the product of this first-stage reaction zone is moved to a second-stage reaction zone where the product is combined with a promoter material and hydrogen and reacted in the presence of a catalyst at a temperature of from 430° C. to 490° C.
Raney catalysts are also known in the art of carbohydrate conversion. For example, U.S. Pat. No. 6,414,201 (issued to Shimazu et al. on Jul. 2, 2002), teaches and claims a process that uses a Raney catalyst formed by melting a mixture of nickel and aluminum and then quenching droplets of the mixture to form a lump alloy, from which particles are broken. However, it is generally known in the art that Raney catalysts work well in static operations, but are not well-adapted to function effectively in continuous processes. Further, similar to the processes using colloid metal, Raney catalysts must be separated and recovered from the reaction mixture at the end of the process.